The treatment of cardiac arrhythmia has changed considerably since the introduction of the technology of catheter ablation by way of high-frequency current. In this technology, an ablation catheter is introduced into one of the heart chambers via veins or arteries under X-ray control and the tissue causing the cardiac arrhythmia is removed by high-frequency current.
The prerequisite for performing a catheter ablation successfully is that the cause of the cardiac arrhythmia is accurately located in the heart chamber. This locating is done via an electrophysiological investigation during which electrical potentials are detected spatially resolved with a mapping catheter introduced into the heart chamber. This electrophysiological investigation, the so-called electroanatomical mapping, thus provides 3D mapping data which can be displayed on a monitor. In many cases, the mapping function and the ablation function are combined in one catheter so that the mapping catheter is also an ablation catheter at the same time.
A known electroanatomical 3D mapping method such as can be performed by way of the carto system by the company Biosense Webster Inc., USA, is based on electromagnetic principles. Underneath the examining table, three different low-intensity alternating magnetic fields are built up. Using integrated electromagnetic sensors at the catheter point of the mapping catheter, it is possible to measure the voltage changes induced by catheter movements within the magnetic field and to calculate the position of the mapping catheter at any time with the aid of mathematical algorithms. Probing the endocardial contour of a heart chamber point by point with the mapping catheter and simultaneously detecting the electrical signals produces an electroanatomical three-dimensional map in which the electrical signals are reproduced color coded.
As a rule, the orientation of the operator required for guiding the catheter has hitherto been effected via fluoroscopic visualization. Since, in electroanatomical mapping, the position of the mapping catheter is known at any time with this technology, the orientation can also take place by continuous representation of the catheter point in the electroanatomical map after a sufficiently large number of measuring points has been detected, so that fluoroscopic imaging technology with X-ray screening can be omitted at this stage.
A fundamental problem in performing the catheter ablation inside the heart is that it has hitherto not been possible to provide optimal orientation of the operator during the guidance of the catheter. A more accurate representation of the morphological environment during the guidance of the catheter which, on the one hand, increase the accuracy during the catheter ablation and, on the other hand, of shortening the time for performing the electroanatomical mapping. Furthermore, the X-ray screening still required for the electroanatomical mapping in many cases could be reduced or avoided in that the X-ray dose applied could also be reduced.
To improve the orientation of the operator when guiding the catheter, different techniques are known. In one technique, a special catheter with an ultrasonic probe is used as is offered, for example, by company Siemens AG Medical Solutions under the title Acunav. Parts of the target tissue to be removed, together with the catheter, can be visualized in real-time via a two-dimensional ultrasonic detection of the environment and of a part of the catheter. However, using such a catheter does not supply three-dimensional image information. The ultrasonic representation can only be used, therefore, in order to insert, for example, a so-called loop catheter into the opening of the pulmonary vein. After the loop catheter has been positioned, tissue removal around the opening of a pulmonary vein can be performed by visualizing both the loop catheter and the ablation catheter by way of X-radiation.
In another known technique, a loop catheter is placed at the opening of the pulmonary vein without the support of imaging 2D ultrasonic technology by applying a contrast medium via a catheter placed in the left atrium in the area of the pulmonary vein opening under X-ray screening. During this process, the contrast medium becomes distributed and a small proportion leaves with the blood flow via the pulmonary vein. This short-time visualization of the pulmonary vein enables the loop catheter to be placed in the opening. The catheter ablation can then be performed as with the above-mentioned technique.
A technique is also known in which the opening of the pulmonary vein is located by electroanatomical mapping of the left atrium and of the pulmonary veins by first introducing the mapping catheter into the pulmonary vein and then pulling it back until electrical activity of the atrium is detected. This position corresponds to the position of the opening of the pulmonary vein around which the target tissue is to be removed.